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Old 16-01-2019, 18:52   #1
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Solar Hot Water System

I've looked for other threads on this subject but haven't found any. From reading European boaty forums their method of heating water is to install a calorifer to use the heat from the exhaust.

But if I want to install a solar hot water system (some time down the track) I wonder why I couldn't use a very small diaphragm pump powered by a solar panel? The solar collector would be a black plastic pipe laying along the gunwale and the storage tank would be an insulated plastic "jerry can".

The idea is not new but I want to avoid the cost the people in the following article incurred.

Getting into hot water and loving it - MySailing.com.au

Any thoughts?

Clive
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Old 16-01-2019, 20:24   #2
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Re: Solar Hot Water System

Would be more efficient and effective (in warm climates) to do a solar thermal collector: mount black panel with copper coils (also painted) and push water through it as needed. They’ve been used for many years and aren’t limited to a he volume in your thermal holding tanks. Only real issue is solar availability, size of collector and exterior temps affecting water output temp, BUT these have been used successfully in cold climates well below freezing and still manage to output heat.
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Old 16-01-2019, 20:46   #3
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Re: Solar Hot Water System

Have a look at Heliatos solar hot water panels and Custom Marine products do a solar hot water collector designed to be mounted under solar panels. senormechanico made a collector integrated into the arch.

Hot water with electricity from solar panels

Heliatos Solar

https://www.custommarineproducts.com...ng-system.html
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Old 16-01-2019, 21:24   #4
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Re: Solar Hot Water System

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Originally Posted by rbk View Post
Would be more efficient and effective (in warm climates) to do a solar thermal collector: mount black panel with copper coils (also painted) and push water through it as needed. They’ve been used for many years and aren’t limited to a he volume in your thermal holding tanks. Only real issue is solar availability, size of collector and exterior temps affecting water output temp, BUT these have been used successfully in cold climates well below freezing and still manage to output heat.

Solar water heaters are very common in Australia: I've got one on my roof and I haven't had to turn the booster on for 4 months now.

I could make the collector up myself but that would take time and where would I mount it? The black tube would be unobtrusive and could be moved to get full sun.

We get lots of sun in Australia but I can see why a solar water heater on a boat in Europe would not be popular. They are absolutely "sold" on their 'Califorers" (heat exchangers)


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Old 16-01-2019, 21:30   #5
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Re: Solar Hot Water System

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Originally Posted by cj88 View Post
Have a look at Heliatos solar hot water panels and Custom Marine products do a solar hot water collector designed to be mounted under solar panels. senormechanico made a collector integrated into the arch.

Hot water with electricity from solar panels

Heliatos Solar

https://www.custommarineproducts.com...ng-system.html

I just had a look at Heliatos Solar and their units are $US799.
That's out of my price range but in line with the figure quoted in the article I gave the link to.

Thanks.


Clive
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Old 16-01-2019, 21:55   #6
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Re: Solar Hot Water System

Perhaps the most practical way to achieve solar hot water is just with your solar electric panels. You're building a big boat and will likely have a good amount of panels. Your charger can trigger a 2PNO relay so when it goes into float the solar output is also connected to a dedicated cheapo Harbor Freight MSW inverter, thus dumping power directly into a calorifier/water heater. Power shedding.

Any electrical engineers out there can comment on this?
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Old 16-01-2019, 22:50   #7
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Re: Solar Hot Water System

Why do you need a pump to circulate the water ?

If you have the storage higher than the heating panel the coldest water will sink to the bottom back into the heating panel where it gets heated and rises to the storage, when it becomes cooler than the water around it, it sinks again.

Take the water to the taps from the top, water supply in at the bottom.

Trapped air will automatically purge when used.
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Old 16-01-2019, 22:58   #8
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Re: Solar Hot Water System

The boat bI purchased to replace my steely has a hot water system with a heat exchanger piped into the engine cooling system and after bathing out of a bucket for 15 years it is fantastic. However, whilst it is great to have a hot shower after about 30 minutes of motoring it's not so good after a day or two at anchor.

My solution is going to be a copper pipe solar heater piped into the hot water tank with a small 12V magnetically coupled centrifugal pump to circulate the heated water through the collector and back into the hot water tank. The hot water system is a pressurized system hence the packerless pump and since the only pressure it will work against is the friction losses in the piping the pump will not have to work against any significant head.

When I remounted the solar panels last year I left a 3" gap down either side and across the back and so will end up with a single loop of 1/2" cupro nickel copper pipe about 30' long with a 1/8" perspex cover over the trough the pipe runs in.

It's going to be interesting to see how effective it will be.
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Old 16-01-2019, 23:06   #9
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Re: Solar Hot Water System

Quote:
Originally Posted by coopec43 View Post
Solar water heaters are very common in Australia: I've got one on my roof and I haven't had to turn the booster on for 4 months now.

I could make the collector up myself but that would take time and where would I mount it? The black tube would be unobtrusive and could be moved to get full sun.

We get lots of sun in Australia but I can see why a solar water heater on a boat in Europe would not be popular. They are absolutely "sold" on their 'Califorers" (heat exchangers)


Clive
Ideally on top of an arch full sun. Your output temp would depend on initial water temp and volume. Ideally a small-ish diameter tube throughout say 5/16 or 1/4” , this would limit volume and keep it running hot and allow for a smaller collector, but also limit the free hot water to sinks (might be impractical to shower with) but it also might be scalding hot. You could increase the pipe diameter and volume but sacrffice higher temps, but increasing the water input temp would help.
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Old 16-01-2019, 23:15   #10
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Re: Solar Hot Water System

Have to say, this, https://www.custommarineproducts.com...ng-system.html looks really interesting, double the function with no real estate loss.
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Old 16-01-2019, 23:21   #11
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Re: Solar Hot Water System

Quote:
Originally Posted by Dave_S View Post
Why do you need a pump to circulate the water ?

If you have the storage higher than the heating panel the coldest water will sink to the bottom back into the heating panel where it gets heated and rises to the storage, when it becomes cooler than the water around it, it sinks again.

Take the water to the taps from the top, water supply in at the bottom.

Trapped air will automatically purge when used.

I need a pump because it will not thermosyphon: the tube "collector" will lay flat on deck and the storage tank would be in the shower recess (maybe below the hand basin?) I definitely do not want a storage tank mounted on deck.



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Old 16-01-2019, 23:25   #12
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Re: Solar Hot Water System

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Originally Posted by makobuilders View Post
Perhaps the most practical way to achieve solar hot water is just with your solar electric panels. You're building a big boat and will likely have a good amount of panels. Your charger can trigger a 2PNO relay so when it goes into float the solar output is also connected to a dedicated cheapo Harbor Freight MSW inverter, thus dumping power directly into a calorifier/water heater. Power shedding.

Any electrical engineers out there can comment on this?
Using solar cells to heat water is not efficient compared to a solar collector.

The most efficient solar cells that are widely available are 18% efficient. A flat plate solar collector is around 60% efficient. Heating water with a collector should be ballpark at least 3 times more efficient than using solar cells to electrically heat water ignoring losses.

However, if the batteries are topped up and especially if you have a dump load controller then who cares how efficient the water heating is because you are basically getting it for free.

To give you an idea of how much water heating you can get. The sun puts out 100 watts per sq ft under ideal conditions. A high efficiency solar cell generates 18 watts per sq ft. 55 sq ft of solar cells is 1000 watts. 1000 watts will heat 10 pounds of water from 60F to 160F in 2.5 hours. A 55 sq ft flat plate solar collector will obviously heat 3+ times that.
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Old 16-01-2019, 23:30   #13
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Re: Solar Hot Water System

Quote:
Originally Posted by Uncle Bob View Post
Have to say, this, https://www.custommarineproducts.com...ng-system.html looks really interesting, double the function with no real estate loss.



WOW!! That looks interesting. Will look into that.


There are different studies of

Solar water heaters Vs solar panels/electricity/heater element

But they take into account life span of units and capital cost which I dion't consider relevant in this situation.

Thanks

Clive
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Old 16-01-2019, 23:46   #14
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Re: Solar Hot Water System

Typical solar heat exchangers don’t use fresh water IN the collector - they heat up coolant and run the hot coolant through a coil in the storage tank. Part of the reason you use coolant is to prevent freeze up or boil-off.

You can get hot water heaters with two coils in them - isotemps, for one. You would typically run a genset’s cooling through the second coil, but you could certainly circulate the hot solar coolant, just as is done on home systems.

One difficulty to take into consideration is that on a house, you’re usually heating a large quantity of water, whereas only 5 or six gallons on a boat - you may have issues with too much heating - your motor has temperature regulation to keep the coolant at 180 or so, so your heater only goes that high, whereas solar could keep climbing ‘till the water in your heater is boiling in hot climates/strong sun, tripping your pressure relief valve. So you have a thermostat shut down the circulation pump when your tank is hot enough, but now your collector is superheated and you could cook on it. You’ll need to figure out something to regulate, or closely monitor and cover the panels when there’s no ‘call’ for heat.

I just found this article about the subject - https://www.radiantcompany.com/system/solar/heatdump/

Let us know how it goes - interesting thread

Cheers,
Matt
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Old 17-01-2019, 00:24   #15
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Re: Solar Hot Water System

Quote:
Originally Posted by mlydon View Post
Typical solar heat exchangers don’t use fresh water IN the collector - they heat up coolant and run the hot coolant through a coil in the storage tank. Part of the reason you use coolant is to prevent freeze up or boil-off.

Let us know how it goes - interesting thread

Cheers,
Matt

You've described my roof-top solar system to a "T". Mine is a closed circuit system with "Hartguard" coolant.

When I turn my garden hose on the water is very hot because it has been lying in the sun. But it is green (not black) and it would lose heat because it has been laying on the ground: but it is still hot....

I've ordered a pump and I have plenty of black tube. I plan to test the idea on the back lawn. If I think it has potential I'll make one up with an insulated storage tank and it will cost very little.


NOTE If you use a solar panel to power the pump you wouldn't have to remember to switch the pump off on sundown as the solar panel would stop generating power.


Clive
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